The present invention relates to a method and apparatus associated with wireless flexural behaviour measurement and in particular, but not exclusively, steady and/or vibrational torque measurement of a shaft of a gas turbine engine for example.
Conventional wireless sensors find a wide range of applications in the area of instrumentation for example in engine development work, processing plants and medicine to name but a few. Wireless sensors have shown a clear potential in particular for vibration and rotational monitoring. When applied for instrumentation on development gas turbine engines, wireless sensors have a number of advantages such as the reduction of expensive wiring, the reduction of complexity, reduced set up time for monitoring and removal of connector faults.
One application of wireless sensors is the measurement of torque on a rotating shaft. The majority of torque sensors employ strain gauges and use slip rings, inductive or optical links to transfer data.
One such torque sensor apparatus 30 is shown on FIG. 1 and comprises an emitter/transceiver 32 directed to a shaft 34 having a metal wire 36 attached thereto. The metal wire is attached between two points on the shaft at an angle to its rotational axis 38. If no torque is applied common in-service vibrations in the shaft excite the string and make it vibrate at its resonance frequency f0, determined by string's geometrical and material parameters. Application of a torque to the shaft alters the string tension, resulting in a corresponding change of the resonance frequency. The microwave transceiver 32, directed towards the sensing wire 44, emits an RF signal which is reflected at the wire 44. The amplitude of the return signal 54 is modulated due to the wire's vibrations. The change of amplitude is indicative of the torque applied to the shaft 34.